Solid-state image pickup element and image pickup apparatus

ABSTRACT

There is provided a solid-state image pickup element including: a photodiode configured to convert incident light into a photocurrent; an amplification transistor configured to amplify a voltage between a gate having a potential depending on the photocurrent and a source having a predetermined reference potential and output the amplified voltage from a drain; and a potential supply section configured to supply an anode of the photodiode and a back-gate of the amplification transistor with a predetermined potential lower than the reference potential.

TECHNICAL FIELD

The present technology relates to a solid-state image pickup element andan image pickup apparatus. Specifically, the present technology relatesto a solid-state image pickup element and an image pickup apparatus thatdetect that the amount of light of a pixel exceeds a threshold.

BACKGROUND ART

From the past, a synchronous solid-state image pickup element that picksup image data (frame) in synchronization with a synchronization signalsuch as a vertical synchronization signal is used in an image pickupapparatus and the like. With this general synchronous solid-state imagepickup element, the image data can be acquired only in each cycle (e.g.,1/60 seconds) of the synchronization signal. Therefore, in a case whereit is necessary to achieve processing at higher speed in the fieldsrelating to traffic, robots, and the like, it is difficult to cope withit. In view of this, a non-synchronous solid-state image pickup elementhas been proposed (e.g., see Patent Literature 1). The non-synchronoussolid-state image pickup element includes an address event detectioncircuit that detects, for each pixel address, that the amount of lightof that pixel exceeds the threshold as an address event in real time.The address event detection circuit is provided in each pixel. In thissolid-state image pickup element, a photodiode and a plurality oftransistors for detecting the address event are arranged for each pixel.

CITATION LIST Patent Literature

PTL 1: Patent Literature 1: Japanese Unexamined Patent ApplicationPublication No. 2016-533140

SUMMARY Technical Problem

With such a non-synchronous solid-state image pickup element, data canbe generated and output at much higher speed than the synchronoussolid-state image pickup element. Therefore, in the traffic field, forexample, the safety can be enhanced by executing image recognitionprocessing for a person or an obstacle at high speed. However, when thereverse bias of the photodiode is lowered due to voltage fluctuationssuch as lowering of a power supply voltage and raising of a groundvoltage, the sensitivity of that photodiode may be lowered and the darkcurrent may increase. Therefore, there is a problem that the signalquality is lowered due to the insufficient sensitivity and the darkcurrent. The sensitivity can be enhanced and the dark current can bereduced by increasing the area of the photodiode. However, the number ofpixels per unit area decreases in that case, and thus it is undesirable.Further, the sensitivity can be enhanced and the dark current can bereduced also by sufficiently increasing the power supply voltage.However, the power consumption increases in that case, and thus it isunfavorable.

The present technology has been produced in view of such circumstancesand it is an object to improve the signal quality of the detectionsignal in the solid-state image pickup element that detects the addressevent.

Solution to Problem

In accordance with a first aspect of the present technology, there isprovided a solid-state image pickup element including: a photodiodeconfigured to convert incident light into a photocurrent; anamplification transistor configured to amplify a voltage between a gatehaving a potential depending on the photocurrent and a source having apredetermined reference potential and output the amplified voltage froma drain; and a potential supply section configured to supply an anode ofthe photodiode and a back-gate of the amplification transistor with apredetermined potential lower than the reference potential. Thisconfiguration provides an effect that the reverse bias of the photodiodeand the threshold voltage of the amplification transistor are increased.

Further, in this first aspect, the solid-state image pickup element mayfurther include a conversion transistor configured to convert thephotocurrent into a voltage between a gate and a source, in which theconversion transistor may include a source which is connected to acathode of the photodiode and the gate of the amplification transistor,and the drain of the amplification transistor may be connected to thegate of the conversion transistor. This configuration provides an effectthat the photocurrent is converted into the voltage.

Further, in this first aspect, the photodiode and the amplificationtransistor may be arranged in each of an effective pixel in which lightis not shielded and a light-shielding pixel in which light is shielded,and the potential supply section may supply the anode of the photodiodecorresponding to the effective pixel with the predetermined potentialand supply the anode of the photodiode corresponding to thelight-shielding pixel with the reference potential. This configurationprovides an effect that a negative potential is supplied only to theeffective pixel.

Further, in this first aspect, the photodiode, the conversiontransistor, and the amplification transistor may be arranged in apredetermined light-receiving board, and the potential supply sectionmay supply the light-receiving hoard with the negative potential. Thisconfiguration provides an effect that the reverse bias of the photodiodeand the threshold voltage of the amplification transistor are increased.

Further, in this first aspect, the solid-state image pickup element mayfurther include a buffer configured to output a voltage signal outputfrom the amplification transistor; a subtractor configured to lower alevel of the voltage signal from the buffer; and a comparator configuredto compare the lowered voltage signal with a predetermined threshold.This configuration provides an effect that an address event is detected.

Further, in this first aspect, the conversion transistor and theamplification transistor may be arranged in a current-to-voltageconversion circuit configured to convert the photocurrent into thevoltage signal, and the current-to-voltage conversion circuit may have apower supply voltage different from a power supply voltage of thebuffer, the subtractor, and the comparator. This configuration providesan effect that a current-to-voltage conversion is performed with a powersupply voltage lower than the power supply voltage of the buffer and thelike.

Further, in this first aspect, the buffer, the subtractor, and thecomparator may include at least a part which is arranged in apredetermined circuit board stacked on the light-receiving board. Thisconfiguration provides an effect that a reverse bias of a photodiode anda threshold voltage of an amplification transistor increase in asolid-state image pickup element having a stacking structure.

Further, in accordance with a second aspect of the present technology,there is provided an image pickup apparatus including: a photodiodeconfigured to convert incident light into a photocurrent; anamplification transistor configured to amplify a voltage between a gatehaving a potential depending on the photocurrent and a source having apredetermined reference potential and output the amplified voltage froma drain; a potential supply section configured to supply an anode of thephotodiode and a back-gate of the amplification transistor with apredetermined potential lower than the reference potential; and a signalprocessing circuit configured to process a signal output from theamplification transistor. This configuration provides an effect that thesignal from the circuit in which the reverse bias of the photodiode andthe threshold voltage of the amplification transistor are increased isprocessed. [Advantageous Effects of Invention]

In accordance with the present technology, an excellent effect that thesignal quality of a detection signal can be improved in a solid-stateimage pickup element that detects an address event can be provided. Itshould be noted that the effect described here are not necessarilylimitative and any effect described in the present disclosure may beprovided.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram depicting a configuration example of an imagepickup apparatus according to an embodiment of the present technology.

FIG. 2 is a diagram for describing a stacking structure of thesolid-state image pickup element according to the embodiment of thepresent technology.

FIG. 3 is an example of a plan view of a light-receiving board accordingto the embodiment of the present technology.

FIG. 4 is an example of a plan view of a circuit board according to theembodiment of the present technology.

FIG. 5 is a block diagram depicting a configuration example of anaddress event detection section according to the embodiment of thepresent technology.

FIG. 6 is a diagram for describing a configuration of an effective pixelaccording to the embodiment of the present technology.

FIG. 7 is a circuit diagram depicting a configuration example of theeffective pixel according to the embodiment of the present technology.

FIG. 8 is an example of a cross-sectional view of effective pixelsaccording to the embodiment of the present technology.

FIG. 9 is an example of a plan view of a pixel array section in amodified example of the embodiment of the present technology.

FIG. 10 is an example of a plan view of a pixel array section obtainedby changing the arrangement of the light-shielding pixel region in themodified example of the embodiment of the present technology.

FIG. 11 is a block diagram depicting an example of schematicconfiguration of a vehicle control system.

FIG. 12 is a diagram of assistance in explaining an example ofinstallation positions of an outside-vehicle information detectingsection and an imaging section.

DESCRIPTION OF EMBODIMENTS

Hereinafter, mode for carrying out the present technology (hereinafter,referred to as embodiment) will be described. Descriptions will be givenin the following order.

1. Embodiment (Example in which negative potential is supplied to anodeof photodiode)

2. Example of Application to Movable Object

1. Embodiment Configuration Example of Image Pickup Apparatus

FIG. 1 is a block diagram depicting a configuration example of an imagepickup apparatus 100 according to the embodiment of the presenttechnology. This image pickup apparatus 100 includes an image pickuplens 110, a solid-state image pickup element 200, a storage unit 120,and a control unit 130. Examples of provided in can include a camera tobe provided in a wearable device, a vehicle-mounted camera, and thelike.

The image pickup lens 110 condenses incident light and introduces thecondensed incident light into the solid-state image pickup element 200.

The solid-state image pickup element 200 detects that an absolute valueof an amount of change of luminance exceeds a threshold for each of aplurality of pixels, as an address event. This address event includes,for example, an on-event indicating that an amount of luminance increaseexceeds an upper-limit threshold and an off-event indicating that anamount of luminance decrease becomes lower than a lower-limit thresholdlower than the upper-limit threshold. Then, the solid-state image pickupelement 200 generates a detection signal indicating the detection resultof the address event for each pixel. Each detection signal includes anon-event detection signal VCH indicating the presence/absence of theon-event and an off-event detection signal VCL indicating thepresence/absence of the off-event. It should be noted that although thesolid-state image pickup element 200 detects the presence/absence ofboth of the on-event and the off-event, the solid-state image pickupelement 200 may detect the presence/absence of only either one of theon-event and the off-event.

The solid-state image pickup element 200 executes predetermined signalprocessing such as image recognition processing on the image dataincluding the detection signal and outputs the processed data to thestorage unit 120 via a signal line 209.

The storage unit 120 stores the data from the solid-state image pickupelement 200. The control unit 130 controls the solid-state image pickupelement 200 to pick up the image data.

Configuration Example of Solid-State Image Pickup Element

FIG. 2 is a diagram depicting an example of a stacking structure of thesolid-state image pickup element 200 according to the embodiment of thepresent technology. This solid-state image pickup element 200 includes acircuit board 202 and a light-receiving board 201 stacked on the circuitboard 202. Those boards are electrically connected to each other via aconnection such as a via-hole. It should be noted that those boards maybe connected to each other by Cu-Cu bonding or with a bump other thanthe via-hole.

FIG. 3 is an example of a plan view of the light-receiving board 201according to the embodiment of the present technology. Thelight-receiving board 201 includes a light-receiving section 220 andvia-hole arrangement sections 211, 212, and 213.

Via-holes to be connected to the circuit board 202 are arranged in thevia-hole arrangement sections 211, 212, and 213. Further, in thelight-receiving section 220, a plurality of light-receiving circuits 221are arranged in a matrix form. The light-receiving circuits 221photoelectrically converts incident light to generate a photocurrent,performs current-to-voltage conversion on that photocurrent, and outputsthe resulting voltage signal. A pixel address including a row addressand a column address is assigned to each of those light-receivingcircuits 221.

FIG. 4 is an example of a plan view of the circuit board 202 accordingto the embodiment of the present technology. This circuit board 202includes a negative-potential supply section 230, via-hole arrangementsections 231, 232, and 233, a signal processing circuit 240, a rowdriving circuit 251, a column driving circuit 252, and an address eventdetection section 260. Via-holes to be connected to the light-receivingboard 201 are arranged in the via-hole arrangement sections 231, 232,and 233.

The negative-potential supply section 230 supplies the light-receivingboard 201 with a predetermined potential lower than a predeterminedreference potential (e.g., ground potential). The predeterminedpotential is supplied as a negative potential. For example, a chargepump circuit is used as the negative-potential supply section 230.Effects provided by suppling the negative potential will be describedlater. It should be noted that the negative-potential supply section 230is an example of a potential supply section defined in the scope ofclaims.

The address event detection section 260 generates a detection signalfrom a voltage signal of each of the plurality of light-receivingcircuits 221 and outputs the generated detection signal to the signalprocessing circuit 240.

The row driving circuit 251 selects a row address and causes the addressevent detection section 260 to output a detection signal correspondingto that row address.

The column driving circuit 252 selects a column address and causes theaddress event detection section 260 to output a detection signalcorresponding to that column address.

The signal processing circuit 240 executes predetermined signalprocessing on detection signals from the address event detection section260. This signal processing circuit 240 arranges detection signals aspixel signals in a matrix form and acquires image data including two-bitinformation for each pixel. Then, the signal processing circuit 240executes signal processing such as image recognition processing on thatimage data.

FIG. 5 is an example of a plan view of the address event detectionsection 260 according to the embodiment of the present technology. Inthis address event detection section 260, a plurality of address eventdetection circuits 261 are arranged in a matrix form. A pixel address isassigned to each of the address event detection circuits 261. Each ofthe address event detection circuits 261 is connected to each of thelight-receiving circuits 221, which has the same address as thecorresponding address event detection circuit 261.

The address event detection circuit 261 quantizes a voltage signal fromthe corresponding light-receiving circuit and outputs the quantizedvoltage signal as a detection signal.

Configuration Example of Effective Pixel

FIG. 6 is a diagram for describing a configuration of an effective pixel310 according to the embodiment of the present technology. The effectivepixel 310 includes the light-receiving circuit 221 inside thelight-receiving board 201 and the address event detection circuit 261inside the circuit board 202, to which the same pixel address isassigned. As described above, in each of the boards, the plurality oflight-receiving circuits 221 and the plurality of address eventdetection circuits 261 are arranged in a matrix form. Therefore, aplurality of effective pixels 310 each including the light-receivingcircuit 221 and the address event detection circuit 261 are arranged ina matrix form in the solid-state image pickup element 200.

FIG. 7 is a circuit diagram depicting a configuration example of theeffective pixel 310 according to the embodiment of the presenttechnology. This effective pixel 310 includes a photodiode 311, acurrent-to-voltage conversion circuit 320, a buffer 330, a subtractor340, a quantizer 350, and a transfer circuit 360.

The photodiode 311 photoelectrically converts incident light to generatea photocurrent. This photodiode 311 supplies the generated photocurrentto the current-to-voltage conversion circuit 320.

The current-to-voltage conversion circuit 320 converts the photocurrentfrom the photodiode 311 into a voltage signal corresponding to thephotocurrent. This current-to-voltage conversion circuit 320 inputs thevoltage signal into the buffer 330.

The buffer 330 outputs the input voltage signal to the subtractor 340.With this buffer 330, driving force for driving a post-stage can beincreased. Further, with the buffer 330, isolation of noise due to aswitching operation at the post-stage can be ensured.

The subtractor 340 determines an amount of change of a correction signalby subtraction. This subtractor 340 supplies the amount of change to thequantizer 350 as a differential signal.

The quantizer 350 converts (in other words, quantizes) an analogdifferential signal into a digital detection signal by comparing thedifferential signal with a predetermined threshold. This quantizer 350compares the differential signal with each of the upper-limit thresholdand the lower-limit threshold and supplies the transfer circuit 360 asthe comparison results thereof as two-bit detection signals. It shouldbe noted that the quantizer 350 is an example of a comparator defined inthe scope of claims.

The transfer circuit 360 transfers the detection signal to the signalprocessing circuit 240 in accordance with a column driving signal fromthe column driving circuit 252.

Further, the current-to-voltage conversion circuit 320 includes N-typetransistors 321 and 322 and a P-type transistor 323. Ametal-oxide-semiconductor (MOS) transistor is used as those transistors,for example.

A source of the N-type transistor 321 is connected to a cathode of thephotodiode 311 and a drain of the N-type transistor 321 is connected toa terminal having a power supply voltage VDD1. The P-type transistor 323and the N-type transistor 322 are connected in series between a terminalhaving a power supply voltage VDD2 and a terminal having a referencepotential (e.g., ground potential GND). Further, a connection pointbetween the P-type transistor 323 and the N-type transistor 322 isconnected to a gate of the N-type transistor 321 and an input terminalof the buffer 330. Further, a predetermined bias voltage Vblog isapplied on a gate of the P-type transistor 323.

The drain of the N-type transistor 321 and a drain of the N-typetransistor 322 are connected to a side of a power supply and such acircuit is called source follower. The N-type transistor 321 of thosetransistors converts a photocurrent into a voltage between the gate andthe source. The N-type transistor 322 amplifies a voltage between a gatehaving a potential depending on the photocurrent and a source having thereference potential (e.g., ground potential GND) and outputs theamplified voltage from the drain. Further, the P-type transistor 323supplies a constant current to the N-type transistor 322. With such aconfiguration, the photocurrent from the photodiode 311 is convertedinto the voltage signal.

It should be noted that the N-type transistor 321 is an example of aconversion transistor defined in the scope of claims and the N-typetransistor 322 is an example of an amplification transistor defined inthe scope of claims.

Further, the photodiode 311 and the N-type transistors 321 and 322 arearranged in the light-receiving board 201 and the circuits following theP-type transistor 323 are arranged in the circuit board 202.

Then, the negative-potential supply section 230 supplies a negativepotential Vn lower than the reference potential (e.g., ground potentialGND) to a P-well region of the light-receiving board 201. The photodiode311 is embedded in this P-well region. Further, back-gates (bulks) ofthe N-type transistors 321 and 322 are formed in that region. Therefore,by supplying the negative potential Vn to the P-well region, thenegative potential Vn can be supplied to an anode of the photodiode 311and the respective back-gates of the N-type transistors 321 and 322.

By setting the anode of the photodiode 311 to have the negativepotential Vn, the reverse bias of the photodiode 311 is larger ascompared to a case where that potential is set to the referencepotential. With this setting, the sensitivity of the photodiode 311 isincreased and the dark current can be reduced. Further, by setting theback-gates of the N-type transistors 321 and 322 to have the negativepotential Vn, a threshold voltage of each transistor is higher due to aboard bias effect as compared to the case where those potentials are setto the reference potential. With this setting, it is possible to preventthe voltages between the gates to the sources of those transistors frombeing equal to or lower than zero. When the voltages between the gatesto the sources are equal to or lower than zero, it may be impossible toobtain a normal output because of the circuit configuration of thecurrent-to-voltage conversion circuit 320. Therefore, such a situationcan be suppressed by supplying the negative potential Vn. In thismanner, the signal quality of the detection signal can be improved dueto the increased sensitivity of the photodiode 311, the reduced darkcurrent, and the higher threshold voltage.

The N-type transistors included in the circuits at the post-stagefollowing the buffer 330 can also be arranged in the P-well regionhaving the negative potential Vn. Even if such a configuration isemployed, it is difficult to obtain the effect in view of thecharacteristics, which have been described in the context of thecurrent-to-voltage conversion operation. Further, it is typicallydesirable that the current-to-voltage conversion circuit 320 be isolatedwhile the circuits at the post-stage are operated having a largeamplitude or a high logic level. It is thus basically favorable toprovide a configuration in which the P-well region on thelight-receiving side is separated from the circuits at the post-stage.

Further, the buffer 330 includes P-type transistors 331 and 332. MOStransistors are used as those transistors, for example.

The P-type transistors 331 and 332 are connected in series between aterminal having the power supply voltage VDD2 and a terminal having thereference potential (e.g., GND). Further, a predetermined bias voltageVbsf is applied on a gate of the P-type transistor 331. A gate of theP-type transistor 332 is connected to an output terminal of thecurrent-to-voltage conversion circuit 320. Then, the voltage signal isoutput to the subtractor 340 from a connection point between the P-typetransistors 331 and 332.

The subtractor 340 includes capacitors 341 and 343, P-type transistors342 and 344, and an N-type transistor 345.

The P-type transistor 344 and the N-type transistor 345 are connected inseries between a terminal having the power supply voltage VDD2 and aterminal having the reference potential. By setting a gate of the P-typetransistor 344 as an input terminal and a connection point between theP-type transistor 344 and the N-type transistor 345 as an outputterminal, the P-type transistor 344 and the N-type transistor 345function as an inverter that inverts an input signal.

One end of the capacitor 341 is connected to an output terminal of thebuffer 330 and the other end of the capacitor 341 is connected to aninput terminal of the inverter (i.e., the gate of the P-type transistor344). The capacitor 343 connected in parallel to the inverter. TheP-type transistor 342 opens/closes a path for connecting both ends ofthe capacitor 343 to each other in accordance with a row driving signal.

When the P-type transistor 342 is turned on, a voltage signal V_(init)is input on a side of the capacitor 341, which is closer to the buffer330, and an opposite side thereof is a virtual ground terminal. For thesake of convenience, the potential of this virtual ground terminal isset to zero. At this time, assuming that the capacitance of thecapacitor 341 is C1, a potential Q_(init) accumulated in the capacitor341 is expressed as an expression below. On the other hand, both ends ofthe capacitor 343 are short-circuited, and thus the accumulated electriccharge is zero.

Q _(init) =C1*V _(init)   Expression 1

Next, assuming a case where the P-type transistor 342 is turned off anda voltage on the side of the capacitor 341, which is closer to thebuffer 330, changes and becomes V_(after), electric charge Q_(after)accumulated in the capacitor 341 is expressed as an expression below.

Q _(after) =C1*V _(after)   Expression 2

On the other hand, assuming that an output voltage is V_(out), electriccharge Q2 accumulated in the capacitor 343 is expressed as an expressionbelow.

Q2=−C2*V _(out)   Expression 3

At this time, a total electric charge amount of the capacitors 341 and343 does not change, and thus an expression below is established.

Q _(init) =Q _(after) +Q2   Expression 4

When Expression 4 is modified by substituting Expressions 1 to 3 intoExpression 4, an expression below is obtained.

V _(out)=−(C1/C2)*(V _(after) −V _(init))   Expression 5

Expression 5 expresses a subtraction operation of the voltage signal andthe gain which is a subtraction result is C1/C2. It is typicallydesirable to maximize the gain. Therefore, it is favorable to set C1 tobe large and C2 to be small. However, when C2 is too small, kTC noiseincreases and a noise characteristic may be deteriorated. Therefore,reduction of the capacitance of C2 is limited to such a range that noisecan be allowed. Further, the subtractor 340 is provided in eacheffective pixel 310. Therefore, the area for the capacitance C1 and C2is limited. In view of those circumstances, for example, C1 is set to avalue of 20 to 200 femtofarads (fF) and C2 is set to a value of 1 to 20femtofarads (fF).

The quantizer 350 includes P-type transistors 351 and 353 and N-typetransistors 352 and 354. MOS transistors are used as those transistors,for example.

The P-type transistor 351 and the N-type transistor 352 are connected inseries between a terminal having the power supply voltage VDD2 and aterminal having the reference potential. The P-type transistor 353 andthe N-type transistor 354 are also connected in series between aterminal having the power supply voltage VDD2 and a terminal having thereference potential. Further, gates of the P-type transistors 351 and353 are connected to an output terminal of the subtractor 340. A biasvoltage Vbon indicating an upper-limit threshold is applied on a gate ofthe N-type transistor 352. A bias voltage Vboff indicating a lower-limitthreshold is applied on a gate of the N-type transistor 354.

A connection point between the P-type transistor 351 and the N-typetransistor 352 is connected to the transfer circuit 360 and a voltage ofthis connection point is output as the on-event detection signal VCH. Aconnection point between the P-type transistor 353 and the N-typetransistor 354 is also connected to the transfer circuit 360 and avoltage of this connection point is output as the off-event detectionsignal VCL. With such connection, the quantizer 350 outputs the on-eventdetection signal VCH at a high level if the differential signal exceedsthe upper-limit threshold and outputs the off-event detection signal VCLat a low level if the differential signal becomes lower than thelower-limit threshold.

It should be noted that although the photodiode 311 and a part of thecurrent-to-voltage conversion circuit 320 are arranged in thelight-receiving board 201 and the circuits at the post-stage thereof arearranged in the circuit board 202, the circuits arranged in therespective chips are not limited to this configuration. For example, thephotodiode 311 and the entire current-to-voltage conversion circuit 320may be arranged in the light-receiving board 201 and other circuits maybe arranged in the circuit board 202. Further, the photodiode 311, thecurrent-to-voltage conversion circuit 320, and the buffer 330 may bearranged in the light-receiving board 201 and other circuits may bearranged in the circuit board 202. Further, the photodiode 311, thecurrent-to-voltage conversion circuit 320, the buffer 330, and thecapacitor 341 may be arranged in the light-receiving board 201 and othercircuits may be arranged in the circuit board 202. Further, thephotodiode 311, the current-to-voltage conversion circuit 320, thebuffer 330, the subtractor 340, and the quantizer 350 may be arranged inthe light-receiving board 201 and other circuits may be arranged in thecircuit board 202.

FIG. 8 is an example of a cross-sectional view of the effective pixels310 according to the embodiment of the present technology. In eachP-well region of the light-receiving board 201, the photodiode 311 isembedded and the back-gates of the N-type transistors 321 and 322 areformed. The drain of the N-type transistor 321 is supplied with thepower supply voltage VDD1 and the potential of the source of the N-typetransistor 322 is the reference potential (e.g., GND). Further, P-wellregions of the adjacent effective pixels 310 are separated from eachother at the long dashed short dashed line.

By supplying the back-gate (bulk) of the N-type transistor 321 with thenegative potential Vn, a high voltage is applied between the drain andthe back-gate as compared to a case where the reference potential isapplied. Typically, regarding the output of the current-to-voltageconversion circuit 320, it is desirable to achieve a large-amplitudeoperation for extending the dynamic range, and it is difficult to lowerthe power supply voltage VDD2 at the post-stage. However, regarding thepower supply voltage VDD1, the dynamic range is not greatly affected.Therefore, it is desirable to set the power supply voltage VDD1 to belower than the power supply voltage VDD2.

The photocurrent from all the effective pixels 310 flows into thenegative-potential supply section 230. If IR drop causes a potentialgradient in the pixel plane, the pixel characteristics themselves mayalso be varied in the plane in a marnner that depends on the IR-drop.Therefore, it is favorable to eliminate the negative potential gradientin the pixel plane by arranging via-holes at a plurality of positions ofthe light-receiving board 201 and the circuit board 202.

As described above, in accordance with the embodiment of the presenttechnology, the reverse bias of the photodiode 311 and the thresholdvoltage can be increased by supplying the negative potential Vn to theanode of the photodiode 311 and the back-gate of the N-type transistor321 or the like. With the increased reverse bias, the sensitivity of thephotodiode 311 can be enhanced and the dark current can be reduced.Further, with the increased threshold voltage, a situation in which itmay be impossible to obtain a normal output can be suppressed.Therefore, the signal quality of the detection signal can be improved.

Modified Example

In the above-mentioned embodiment, the negative-potential supply section230 supplies the negative potential Vn to all the pixels. However, thepower consumption may increase as the number of pixels increases. Asolid-state image pickup element 200 according to this modified exampleis different from the above-mentioned embodiment in that thelight-shielding pixel is not supplied with the negative potential Vn.

FIG. 9 is an example of a plan view of a pixel array section 300 in themodified example of the embodiment of the present technology. This pixelarray section 300 includes a light-receiving section 220 and an addressevent detection section 260 which are stacked on each other. The pixelarray section 300 includes horizontal light-shielding pixel regions 301and 303 and an effective pixel region 302.

The plurality of effective pixels 310 are arranged in a matrix form inthe effective pixel region 302. Light is not shielded in those pixels.

On the other hand, a plurality of light-shielding pixels 315 arearranged in a matrix form each of the horizontal light-shielding pixelregions 301 and 303. Light is shielded in those pixels. Further, columnaddresses different from those of effective pixels 310 are assigned tolight-shielding pixels 315 within the horizontal light-shielding pixelregions 301 and 303. Further, a circuit configuration of thelight-shielding pixels 315 is similar to the effective pixels 310.

The negative-potential supply section 230 supplies a negative potentialVn1 to the P-well region of the effective pixel 310. On the other hand,the negative-potential supply section 230 supplies a potential Vn2 suchas the reference potential (GND) to P-well regions of thelight-shielding pixels 315.

The signal processing circuit 240 and the circuits at the post-stagethereof determine a dark current amount on the basis of pixel signalsfrom the light-shielding pixels 315 and remove the dark current in pixelsignals from the effective pixels 310.

It should be noted that although the horizontal light-shielding pixelregions 301 and 303 are arranged, a vertical light-shielding pixelregion 304 may be arranged instead of the horizontal light-shieldingpixel regions 301 and 303, as illustrated in FIG. 10. Row addressesdifferent from those of the effective pixels 310 are assigned to thelight-shielding pixels 315 within this vertical light-shielding pixelregion 304. Further, both of the horizontal light-shielding pixelregions 301 and 303 and the vertical light-shielding pixel region 304may be arranged.

As described above, in accordance with the modified example of theembodiment of the present technology, the negative-potential supplysection 230 supplies the negative potential Vn1 only to the effectivepixels 310 of all the pixels. The power consumption can thus be reducedas compared to the case where the negative potential Vn1 is supplied toall the pixels.

Example of Application to Movable Object

The technology (present technology) according to the present disclosurecan be applied to various products. For example, the technologyaccording to the present disclosure may be realized as a device mountedon any kind of movable objects such as a car, an electric car, a hybridelectric car, a motorcycle, a bicycle, a personal mobility, an aircraft,a drone, a ship, and a robot.

FIG. 11 is a block diagram depicting an example of schematicconfiguration of a vehicle control system as an example of a mobile bodycontrol system to which the technology according to an embodiment of thepresent disclosure can be applied.

The vehicle control system 12000 includes a plurality of electroniccontrol units connected to each other via a communication network 12001.In the example depicted in FIG. 11, the vehicle control system 12000includes a driving system control unit 12010, a body system control unit12020, an outside-vehicle information detecting unit 12030, anin-vehicle information detecting unit 12040, and an integrated controlunit 12050. In addition, a microcomputer 12051, a sound/image outputsection 12052, and a vehicle-mounted network interface (I/F) 12053 areillustrated as a functional configuration of the integrated control unit12050.

The driving system control unit 12010 controls the operation of devicesrelated to the driving system of the vehicle in accordance with variouskinds of programs. For example, the driving system control unit 12010functions as a control device for a driving force generating device forgenerating the driving force of the vehicle, such as an internalcombustion engine, a driving motor, or the like, a driving forcetransmitting mechanism for transmitting the driving force to wheels, asteering mechanism for adjusting the steering angle of the vehicle, abraking device for generating the braking force of the vehicle, and thelike.

The body system control unit 12020 controls the operation of variouskinds of devices provided to a vehicle body in accordance with variouskinds of programs. For example, the body system control unit 12020functions as a control device for a keyless entry system, a smart keysystem, a power window device, or various kinds of lamps such as aheadlamp, a backup lamp, a brake lamp, a turn signal, a fog lamp, or thelike. In this case, radio waves transmitted from a mobile device as analternative to a key or signals of various kinds of switches can beinput to the body system control unit 12020. The body system controlunit 12020 receives these input radio waves or signals, and controls adoor lock device, the power window device, the lamps, or the like of thevehicle.

The outside-vehicle information detecting unit 12030 detects informationabout the outside of the vehicle including the vehicle control system12000. For example, the outside-vehicle information detecting unit 12030is connected with an imaging section 12031. The outside-vehicleinformation detecting unit 12030 makes the imaging section 12031 imagean image of the outside of the vehicle, and receives the imaged image.On the basis of the received image, the outside-vehicle informationdetecting unit 12030 may perform processing of detecting an object suchas a human, a vehicle, an obstacle, a sign, a character on a roadsurface, or the like, or processing of detecting a distance thereto.

The imaging section 12031 is an optical sensor that receives light, andwhich outputs an electric signal corresponding to a received lightamount of the light. The imaging section 12031 can output the electricsignal as an image, or can output the electric signal as informationabout a measured distance. In addition, the light received by theimaging section 12031 may be visible light, or may be invisible lightsuch as infrared rays or the like.

The in-vehicle information detecting unit 12040 detects informationabout the inside of the vehicle. The in-vehicle information detectingunit 12040 is, for example, connected with a driver state detectingsection 12041 that detects the state of a driver. The driver statedetecting section 12041, for example, includes a camera that images thedriver. On the basis of detection information input from the driverstate detecting section 12041, the in-vehicle information detecting unit12040 may calculate a degree of fatigue of the driver or a degree ofconcentration of the driver, or may determine whether the driver isdozing.

The microcomputer 12051 can calculate a control target value for thedriving force generating device, the steering mechanism, or the brakingdevice on the basis of the information about the inside or outside ofthe vehicle which information is obtained by the outside-vehicleinformation detecting unit 12030 or the in-vehicle information detectingunit 12040, and output a control command to the driving system controlunit 12010. For example, the microcomputer 12051 can perform cooperativecontrol intended to implement functions of an advanced driver assistancesystem (ADAS) which functions include collision avoidance or shockmitigation for the vehicle, following driving based on a followingdistance, vehicle speed maintaining driving, a warning of collision ofthe vehicle, a warning of deviation of the vehicle from a lane, or thelike.

In addition, the microcomputer 12051 can perform cooperative controlintended for automatic driving, which makes the vehicle to travelautonomously without depending on the operation of the driver, or thelike, by controlling the driving force generating device, the steeringmechanism, the braking device, or the like on the basis of theinformation about the outside or inside of the vehicle which informationis obtained by the outside-vehicle information detecting unit 12030 orthe in-vehicle information detecting unit 12040.

In addition, the microcomputer 12051 can output a control command to thebody system control unit 12020 on the basis of the information about theoutside of the vehicle which information is obtained by theoutside-vehicle information detecting unit 12030. For example, themicrocomputer 12051 can perform cooperative control intended to preventa glare by controlling the headlamp so as to change from a high beam toa low beam, for example, in accordance with the position of a precedingvehicle or an oncoming vehicle detected by the outside-vehicleinformation detecting unit 12030.

The sound/image output section 12052 transmits an output signal of atleast one of a sound and an image to an output device capable ofvisually or auditorily notifying information to an occupant of thevehicle or the outside of the vehicle. In the example of FIG. 11, anaudio speaker 12061, a display section 12062, and an instrument panel12063 are illustrated as the output device. The display section 12062may, for example, include at least one of an on-board display and ahead-up display.

FIG. 12 is a diagram depicting an example of the installation positionof the imaging section 12031.

In FIG. 12, the imaging section 12031 includes imaging sections 12101,12102, 12103, 12104, and 12105.

The imaging sections 12101, 12102, 12103, 12104, and 12105 are, forexample, disposed at positions on a front nose, sideview mirrors, a rearbumper, and a back door of the vehicle 12100 as well as a position on anupper portion of a windshield within the interior of the vehicle. Theimaging section 12101 provided to the front nose and the imaging section12105 provided to the upper portion of the windshield within theinterior of the vehicle obtain mainly an image of the front of thevehicle 12100. The imaging sections 12102 and 12103 provided to thesideview mirrors obtain mainly an image of the sides of the vehicle12100. The imaging section 12104 provided to the rear bumper or the backdoor obtains mainly an image of the rear of the vehicle 12100. Theimaging section 12105 provided to the upper portion of the windshieldwithin the interior of the vehicle is used mainly to detect a precedingvehicle, a pedestrian, an obstacle, a signal, a traffic sign, a lane, orthe like.

Incidentally, FIG. 12 depicts an example of photographing ranges of theimaging sections 12101 to 12104. An imaging range 12111 represents theimaging range of the imaging section 12101 provided to the front nose.Imaging ranges 12112 and 12113 respectively represent the imaging rangesof the imaging sections 12102 and 12103 provided to the sideviewmirrors. An imaging range 12114 represents the imaging range of theimaging section 12104 provided to the rear bumper or the back door. Abird's-eye image of the vehicle 12100 as viewed from above is obtainedby super-imposing image data imaged by the imaging sections 12101 to12104, for example.

At least one of the imaging sections 12101 to 12104 may have a functionof obtaining distance information. For example, at least one of theimaging sections 12101 to 12104 may be a stereo camera constituted of aplurality of imaging elements, or may be an imaging element havingpixels for phase difference detection.

For example, the microcomputer 12051 can determine a distance to eachthree-dimensional object within the imaging ranges 12111 to 12114 and atemporal change in the distance (relative speed with respect to thevehicle 12100) on the basis of the distance information obtained fromthe imaging sections 12101 to 12104, and thereby extract, as a precedingvehicle, a nearest three-dimensional object in particular that ispresent on a traveling path of the vehicle 12100 and which travels insubstantially the same direction as the vehicle 12100 at a predeterminedspeed (for example, equal to or more than 0 km/hour). Further, themicrocomputer 12051 can set a following distance to be maintained infront of a preceding vehicle in advance, and perform automatic brakecontrol (including following stop control), automatic accelerationcontrol (including following start control), or the like. It is thuspossible to perform cooperative control intended for automatic drivingthat makes the vehicle travel autonomously without depending on theoperation of the driver or the like.

For example, the microcomputer 12051 can classify three-dimensionalobject data on three-dimensional objects into three-dimensional objectdata of a two-wheeled vehicle, a standard-sized vehicle, a large-sizedvehicle, a pedestrian, a utility pole, and other three-dimensionalobjects on the basis of the distance information obtained from theimaging sections 12101 to 12104, extract the classifiedthree-dimensional object data, and use the extracted three-dimensionalobject data for automatic avoidance of an obstacle. For example, themicrocomputer 12051 identifies obstacles around the vehicle 12100 asobstacles that the driver of the vehicle 12100 can recognize visuallyand obstacles that are difficult for the driver of the vehicle 12100 torecognize visually. Then, the microcomputer 12051 determines a collisionrisk indicating a risk of collision with each obstacle. In a situationin which the collision risk is equal to or higher than a set value andthere is thus a possibility of collision, the microcomputer 12051outputs a warning to the driver via the audio speaker 12061 or thedisplay section 12062, and performs forced deceleration or avoidancesteering via the driving system control unit 12010. The microcomputer12051 can thereby assist in driving to avoid collision.

At least one of the imaging sections 12101 to 12104 may be an infraredcamera that detects infrared rays. The microcomputer 12051 can, forexample, recognize a pedestrian by determining whether or not there is apedestrian in imaged images of the imaging sections 12101 to 12104. Suchrecognition of a pedestrian is, for example, performed by a procedure ofextracting characteristic points in the imaged images of the imagingsections 12101 to 12104 as infrared cameras and a procedure ofdetermining whether or not it is the pedestrian by performing patternmatching processing on a series of characteristic points representingthe contour of the object. When the microcomputer 12051 determines thatthere is a pedestrian in the imaged images of the imaging sections 12101to 12104, and thus recognizes the pedestrian, the sound/image outputsection 12052 controls the display section 12062 so that a squarecontour line for emphasis is displayed so as to be superimposed on therecognized pedestrian. The sound/image output section 12052 may alsocontrol the display section 12062 so that an icon or the likerepresenting the pedestrian is displayed at a desired position.

Hereinabove, the example of the vehicle control system to which thetechnology according to the present disclosure can be applied has beendescribed. The technology according to the present disclosure can beapplied to the imaging section 12031 of the above-mentionedconfigurations. Specifically, the image pickup apparatus 100 of FIG. 1can be applied to the imaging section 12031. By applying the technologyaccording to the present disclosure to the imaging section 12031, thesignal quality of the detection signal can be improved. Therefore, theaccuracy of image recognition or the like using a detection signal canbe improved.

Note that the above-mentioned embodiments provide examples for embodyingthe present technology and the matters in the embodiments and theinvention-specifying matters in the scope of claims are associated.Similarly, the invention-specifying matters in the scope of claims andthe matters in the embodiments of the present technology, which aredenoted by the identical names, have correspondence. It should be notedthat the present technology is not limited to the embodiments and can beembodied by making various modifications to the embodiments withoutdeparting from its essence.

It should be noted that the effects described in the specification aremerely exemplary and are not limitative and other effects may beprovided.

It should be noted that the present technology may also take thefollowing configurations.

(1) A solid-state image pickup element, including:

a photodiode configured to convert incident light into a photocurrent;

an amplification transistor configured to amplify a voltage between agate having a potential depending on the photocurrent and a sourcehaving a predetermined reference potential and output the amplifiedvoltage from a drain; and

a potential supply section configured to supply an anode of thephotodiode and a back-gate of the amplification transistor with apredetermined potential lower than the reference potential.

(2) The solid-state image pickup element according to (1), furtherincluding

a conversion transistor configured to convert the photocurrent into avoltage between a gate and a source, in which

the conversion transistor includes a source which is connected to acathode of the photodiode and the gate of the amplification transistor,and

the drain of the amplification transistor is connected to the gate ofthe conversion transistor.

(3) The solid-state image pickup element according to (2), in which

the photodiode and the amplification transistor are arranged in each ofan effective pixel in which light is not shielded and a light-shieldingpixel in which light is shielded, and

the potential supply section supplies the anode of the photodiodecorresponding to the effective pixel with the predetermined potentialand supplies the anode of the photodiode corresponding to thelight-shielding pixel with the reference potential.

(4) The solid-state image pickup element according to (2) or (3), inwhich

the photodiode, the conversion transistor, and the amplificationtransistor are arranged in a predetermined light-receiving board, and

the potential supply section supplies the light-receiving board with thepredetermined potential.

(5) The solid-state image pickup element according to (4), furtherincluding

a buffer configured to output a voltage signal output from theamplification transistor;

a subtractor configured to lower a level of the voltage signal from thebuffer; and

a comparator configured to compare the lowered voltage signal with apredetermined threshold.

(6) The solid-state image pickup element according to (5), in which

the conversion transistor and the amplification transistor are arrangedin a current-to-voltage conversion circuit configured to convert thephotocurrent into the voltage signal, and

the current-to-voltage conversion circuit has a power supply voltagedifferent from a power supply voltage of the buffer, the subtractor, andthe comparator.

(7) The solid-state image pickup element according to (5) or (6), inwhich

the buffer, the subtractor, and the comparator include at least a partwhich is arranged in a predetermined circuit board stacked on thelight-receiving board.

(8) An image pickup apparatus, including:

a photodiode configured to convert incident light into a photocurrent;

an amplification transistor configured to amplify a voltage between agate having a potential depending on the photocurrent and a sourcehaving a predetermined reference potential and output the amplifiedvoltage from a drain;

a potential supply section configured to supply an anode of thephotodiode and a back-gate of the amplification transistor with apredetermined potential lower than the reference potential; and

a signal processing circuit configured to process a signal output fromthe amplification transistor.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

REFERENCE SIGNS LIST

100 Image pickup apparatus

110 Image pickup lens

120 Storage unit

130 Control unit

200 Solid-state image pickup element

201 Light-receiving board

202 Circuit board

211, 212, 213, 231, 232, 233 Via-hole arrangement section

220 Light-receiving section

221 Light-receiving circuit

230 Negative-potential supply section

240 Signal processing circuit

251 Row driving circuit

252 Column driving circuit

260 Address event detection section

261 Address event detection circuit

300 Pixel array section

310 Effective pixel

311 Photodiode

315 Light-shielding pixel

320 Current-to-voltage conversion circuit

321, 322, 345, 352, 354 N-type transistor

323, 331, 332, 342, 344, 351, 353 P-type transistor

330 Buffer

340 Subtractor

341, 343 Capacitor

350 Quantizer

360 Transfer circuit

12031 Imaging section

1. A solid-state image pickup element, comprising: a photodiodeconfigured to convert incident light into a photocurrent; anamplification transistor configured to amplify a voltage between a gatehaving a potential depending on the photocurrent and a source having apredetermined reference potential and output the amplified voltage froma drain; and a potential supply section configured to supply an anode ofthe photodiode and a back-gate of the amplification transistor with apredetermined potential lower than the reference potential.
 2. Thesolid-state image pickup element according to claim 1, furthercomprising a conversion transistor configured to convert thephotocurrent into a voltage between a gate and a source, wherein theconversion transistor includes a source which is connected to a cathodeof the photodiode and the gate of the amplification transistor, and thedrain of the amplification transistor is connected to the gate of theconversion transistor.
 3. The solid-state image pickup element accordingto claim 2, wherein the photodiode and the amplification transistor arearranged in each of an effective pixel in which light is not shieldedand a light-shielding pixel in which light is shielded, and thepotential supply section supplies the anode of the photodiodecorresponding to the effective pixel with the predetermined potentialand supplies the anode of the photodiode corresponding to thelight-shielding pixel with the reference potential.
 4. The solid-stateimage pickup element according to claim 2, wherein the photodiode, theconversion transistor, and the amplification transistor are arranged ina predetermined light-receiving board, and the potential supply sectionsupplies the light-receiving board with the predetermined potential. 5.The solid-state image pickup element according to claim 4, furthercomprising a buffer configured to output a voltage signal output fromthe amplification transistor; a subtractor configured to lower a levelof the voltage signal from the buffer; and a comparator configured tocompare the lowered voltage signal with a predetermined threshold. 6.The solid-state image pickup element according to claim 5, wherein theconversion transistor and the amplification transistor are arranged in acurrent-to-voltage conversion circuit configured to convert thephotocurrent into the voltage signal, and the current-to-voltageconversion circuit has a power supply voltage different from a powersupply voltage of the buffer, the subtractor, and the comparator.
 7. Thesolid-state image pickup element according to claim 5, wherein thebuffer, the subtractor, and the comparator include at least a part whichis arranged in a predetermined circuit board stacked on thelight-receiving board.
 8. An image pickup apparatus, comprising: aphotodiode configured to convert, incident light into a photocurrent; anamplification transistor configured to amplify a voltage between a gatehaving a potential depending on the photocurrent and a source having apredetermined reference potential and output the amplified voltage froma drain; a potential supply section configured to supply an anode of thephotodiode and a back-gate of the amplification transistor with apredetermined potential lower than the reference potential; and a signalprocessing circuit configured to process a signal output from theamplification transistor.